What if bitcoin comes with 0 USD ?
To answer your question I will have to ask you another question. How many people do you think bought bitcoins since it crossed 1000$ mark ? If you bought some BTC at 1000$ what will be reaction when you see it at 10$. One you would feel sad that your investment is not rewarding you as much as it should, second thing that would cross your mind is "this thing did rise to 10000$ in the past so what if I buy as much as I can and forget about it for the coming 5 years." the hidden gambler in you will take control and you will buy as much as you can.
This second thought would be common in all BTC holders. If it comes down to say 10$ people are going to buy it like crazy and when they do, the price will bounce back to something much more higher in the coming years.
A large number of investors today are institutional investors or simply people who are too rich. For eg The Winklevoss Twins who hold more than 11 Million $ in bitcoins which they bought in at 120$. If BTC comes down to 10$ what do you think they will do ?